Insecticidal effect of Keepdry® for the control of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) on wheat under laboratory conditions

Abstract

Laboratory bioassays were conducted to evaluate the insecticidal efficacy of the diatomaceous earth (DE) Keepdry® grain protectant against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) adults. Factors such as dose (50, 100, 200 and 500 ppm), exposure interval (7, 14 and 21 d), relative humidity (r.h.) (55 and 75%) and temperature (20, 25 and 30 °C) were tested. Progeny production was assessed 60 d after the removal of parental adults. For R. dominica, after 7 d of exposure, mortality was increased with the increase of temperature in most of the tested combinations. At 30 °C the mortality of R. dominica adults was higher at 55% r.h. than at 75% r.h. on wheat treated with 500 ppm DE. At 30 °C and 55% r.h., 86.7% of the exposed R. dominica adults were dead after 14 d of exposure and all were dead after 21 d of exposure. With 500 ppm of DE at 30 °C and 75% r.h., mortality reached only 83% after 21 d of exposure. Regarding progeny production, the increase of temperature and r.h. increased adult emergence. For S. oryzae, after 7 d of exposure, mortality was increased with the increase of temperature and decreased with the increase of r.h. in the majority of the combinations tested. At the highest dose, mortality at 25 and 30 °C was >96%, in all cases. At the highest dose, all adults were dead at 30 °C and 55% r.h. after 14 d of exposure. Progeny was completely suppressed at 20 °C and 55% r.h. and 50, 200 or 500 ppm. The results of the present study show that Keepdry® is effective at doses that are lower than other commercially available DEs, for the control of R. dominica and S. oryzae, taking into consideration that its efficacy is influenced by the abiotic factors temperature and r.h.